Batboard

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This forum is dedicated to helping people with questions about installing radio equipment in vehicles. This can include antenna installs, electrical wiring questions/problems, and mounting systems. Pictures of installs are welcome.

Note: Discussions regarding lighting, sirens, and other equipment now has its own forum in the 'off-topic' section below.

Unless the truck batteries are new, it is not a good idea to center tap the two 12 volt batteries at the center point where you would expect to find 12 volts. This point is only 12 volts under a low current draw condition. As current input or output goes up, this 12 volt point can fly around and be either low or high in voltage. Bottom line it is only 12 volts if both batteries have a low internal resistance.

The problem compounds itself as the batteries age. The internal resistance goes up and the voltage filtering ability of the batteries goes down. As this happens, the ability of each battery to hold the mid point tap goes lower. As an example, if you go to start the truck engine, this mid point tap voltage could go real low or even high due to the high current draw from the starter motor. Once the engine starts, the charging alternator will try to bring the total electrical system 24 volt voltage back to normal. If the low side battery that has one terminal grounded, has lost it's low internal resistance, there is the possibility that you might even see close to the 24 volts at this mid point tap.

As has already been mentioned, using a voltage converter power module is the way to go. These units are made to take the full 24 volt input and convert it to the 12 volts the radio requires. It doesn't rely on any battery internal resistance to keep the voltage going to the radio at 12 volts.

I have used the 24 volt to 12 volt converter power modules on many large trucks and big front end loaders. Never had a radio problem once they were installed. Just make sure you get one large enough to carry the transmitter current demand.